The present invention pertains to the field of mobile elevationally adjustable folding stages, and to improvements therein. Stages generally of this type having come into wide-spread use in schools, hotels, convention centers, and other institutions wherein multiple use facilities require the capability of setting up a temporary stage. Such stages are made up of a number of individual sections which are positioned adjacent each other to make an extended stage surface of whatever size is required. When not in use, the individual sections may be folded to compact dimensions, then set aside for storage. Most such stages are made up of at least two stage surface members hinged together to allow the folding action, and have legs which are also pivoted to either fold out of the way or to remain in floor contact position while the stage surfaces fold to the stage position. Often wheels are provided to make the stage section mobile, so that it can be more easily transported from the use area to a storage area.
Elevationally adjustable folding stages have recently been developed to further increase the utility of the folding stage concept. Examples of such developments are found in copending United States patent application Ser. No. 626,979, invented by Kermit H. Wilson, Richard C. Bue and Ronald R. Carlson, now Patent 4,026,221 and Ser. No. 638,167, invented by Kermit H. Wilson, now Patent 3,999,491. Although the stages developed to date have been very successful in achieving their object of providing efficient and useful stages, further improvements are of course still possible, particularly with regard to stages having a very high maximum height, and also in regard to improving the convenience and efficiency in setting up the stage for use.
With regard to the maximum height of the stage, some designs which perform very well in small stages, or ones with a limited range of elevational adjustment, do not readily lend themselves to larger or higher stages, in part because of the need for increased rigidity to prevent swaying or shaking in a tall stage section. Of course all parts can be proportionately strengthened, but the resulting structure is not necessarily the most efficient in terms of weight, cost and difficulty of handling. The present invention provides a stage which is especially advantageous in stages of great height and load carrying capability, although it is equally well adapted for smaller stages.
The wheels in mobile folding stages are provided as a convenience in moving the stage to and from the storage area, but some means must be provided to insure that the stage is not free to move while being used in its operative position. Locking type arrangements on castor wheels are generally unsatisfactory for stages which must hold any appreciable amount of weight, or for active loads, such as persons, rather than mere static loads. For this reason retraction mechanisms have been developed whereby the wheels extend slightly lower than the leg when the stage is folded up, but are retracted to slightly shorter than the legs when the stage is in use, so that the full weight of the load is borne on the legs rather than the wheels. In prior art stages, wheel retraction has been tied to the unfolding of the stage, either by a special linkage connected from the folding stage mechanism to the wheels, or by means of the geometry of the leg/wheel assembly which changes during unfolding to pivot the wheel out of ground contact. Since either method relies on the unfolding of the stage for retracting the wheels, the disadvantage arises in that it is impossible to exactly position the stage while it is still on its wheels.
For example, if a number of stage sections are being juxtaposed to form a large stage, it is necessary that each stage surface abut the adjacent one, so that no gaps are left. The folded prior art stage may be wheeled into approximate position, but final adjustment of the position will be necessary after it is fully unfolded since it is impossible to guess the exact location while the stage is still folded. But at the time the adjustment in position is necessary, the wheels have already been retracted, requiring one or two workers to lift and reposition the stage.
The present invention provides a manually actuated retraction/extension mechanism for the wheels which is independent of the folding or unfolding of the stage. Thus, the stage may be unfolded to operating position, then easily wheeled exactly into position before retracting the wheels to transfer weight to the legs. When setting up a large number of stage sections, the resulting increased efficiency can result in a substantial savings of time and effort.
The present invention further improves over prior art stages by permitting the stage to be folded for storage without first having to lower the stage to its lowest position. With some prior art stages, it was necessary to first lower the stage at least from its highest position before it could be folded for storage. This presents additional unnecessary handling time for a user who usually needs the stages set up in an extended position.
The present invention, by providing center support legs, by maintaining the main support legs substantially vertical when unfolded, and by providing adjustable cross braces, achieves a great height extension capability and load bearing capability from a lighter, stronger and more efficient structure.
Locking means for securing the stage in its unfolded, operative position are also provided in the present invention. In the preferred embodiment, the locking means operates in conjunction with the hinged connection between the stage surface members. The locking means performs the primary function of preventing the stage from starting to fold when loads are placed on the ends of the stage surfaces. The lock also performs a secondary function in permitting the unfolded stage to be lifted and supported by a fork lift while the legs are being elevationally adjusted.
In the preferred embodiment, the actuating lever for the locking means is positioned at the side of the stage so that it projects upwards alongside the edge of the stage when in its unlocked position. This prevents an unlocked stage section from being inadvertently moved in position immediately adjacent another to form a large stage surface. The upward projecting locking lever thus serves as a reminder that the stage must be locked before use.